Fine-Tuned for Life

John Leslie

The Life of the Cosmos by Lee Smolin
Weidenfeld, 358 pp, £20.00, September 1997, ISBN 0 297 81727 2

Our expanding universe has existed for roughly ten billion years. Even to get from Earth’s formation to our century took as long, Martin Rees remarks, as journeying half across America at the rate of one step per two thousand years. Our sun will shine steadily for five billion more years before swelling and vaporising our planet. The universe, however, will probably last for at least another hundred billion. It is widely expected to collapse eventually, but might first dilate by a factor of one followed by a million zeroes. Its expansion is possible even if it has always been infinitely large. Infinitely many galaxies, scattered across infinite space, could keep getting further apart. Infinity being a large number, some of the galaxies could well contain exact duplicates of you and me, Rees points out. With sufficiently many typing monkeys, even Hamlet would get typed many times.

The universe might perhaps expand eternally, becoming ever colder. Given enough time, strange things could happen. An electron could find its motions controlled by an equally insignificant positron tugging at it ever so weakly from ten billion light years away. (A light year is roughly ten trillion kilometres.) After a number of centuries so great that its zeroes were as many as all the atoms within reach of our telescopes, neutron stars would collapse to black holes – entities so dense that even light rays cannot overcome their gravitational pull – through their parts suddenly chancing to rush together, as quantum theory allows. Conceivably, though, only another fifty billion years separate us from a time when everything will start collapsing towards a Big Crunch. Its violence would rival the Big Bang in which the universe began – or which at least opened the cosmic period known to us.

Rees’s pages survey these and many more marvels. The material of the expanding universe is already very thinly spread. It is as if a snowflake’s atoms had dispersed through a region as large as the Earth. Some ten billion years ago, in contrast, everything detectable by our telescopes occupied a volume no bigger than a golf ball, undergoing random fluctuations which gave rise to entire galaxies later. Smaller fluctuations perhaps generated black holes tiny enough to fit inside atomic nuclei, yet each as massive as a mountain. These might nowadays be ending their ‘black hole evaporation’ (a process discovered by Stephen Hawking) in bangs detectable from two million light years away. Bigger black holes, their evaporation too slow to be detected, probably litter our galaxy in large numbers as the remnants of stellar explosions.

Other such remnants are neutron stars. Roughly the size of a town, they are so compact – at some hundred million tons to the teaspoonful – that they can rotate hundreds of times a second without flying apart. The resulting rapid pulses at radio wavelengths were jocularly referred to as ‘LGM’, meaning ‘little green men’, before their true nature was confirmed. The stellar explosions themselves, ‘supernovas’, scatter the products of stellar cookery (nucleosynthesis) so that planets and persons can be made from them. Our bodies contain atoms cooked inside many stars, some not even in our galaxy.

All these wonders have been discovered with technology yet more wondrous. A century and a half ago, Auguste Comte cited the composition of the stars as something which would never be known. Astronomers now determine it by analysing starlight. Helium was discovered by this means before being recognised on Earth. The sky’s radio waves, too, are remarkably informative. Linked across a continent, radio telescopes act like a single gigantic dish. Each operates with superb efficiency. All the energy it will ever have collected for astronomers to analyse is less than is needed for picking up a cigarette. Gravitational waves have been detected through the star movements they cause, slower than the hour hand of a watch. Even neutron star ‘starquakes’ of a few micrometres (thousandths of a millimetre) have been detected.

Rees, the Astronomer Royal, is a combination of theoretician and observer. Only heavy contributions from theory allow micrometre-sized starquakes to be ‘seen’: deduced, that is to say, from tiny variations in a neutron star’s rotation. In the same way, we can ‘see’ a Big Bang, but not a universe which has existed eternally in a Steady State with new matter constantly being created to fill its expanding space. One of Rees’s first projects was counting distant radio sources, now thought to be regions where matter is swallowed by gigantic black holes. He found too many to fit comfortably into a Steady State universe.

He gives odds of only about ten to one in favour of a hot Big Bang, however – a sign of considerable open-mindedness, almost everyone else being much more firmly convinced. His attitude towards ‘dark matter’ is similar. Our galaxy is held together gravitationally by far more matter than is actually visible. The protons, neutrons and electrons which make stones and trees and rabbits are probably comparatively rare, over 90 per cent of the galaxy being ‘dark’ material with unknown components. Rees is a leading advocate of the idea that slow-moving ‘cold dark matter’ encouraged galaxies to form. Even though this theory is now winning, he is quick to say that the ‘hot dark matter’ of his competitors could help.

As he stresses, investigating such questions can be fruitful for physics. The highest energies physicists can yet produce are trillions of times below the Big Bang energies at which the elegance of Nature’s laws stands most fully revealed. They therefore ask astronomers for evidence left behind by the Ultimate High Energy Experiment, conducted some ten billion years ago in an exploding laboratory.

Before the Beginning is at its finest when discussing life’s place in the universe. Recent findings challenge the notion that Nature’s fundamental laws, the ones reigning at ultrahigh energies, completely dictate the physics of our low-energy surroundings. There are signs that such things as the strengths of physical forces (gravity and electromagnetism, for instance) and the masses of elementary particles (such as the proton and electron) differ randomly from one to another of vastly many regions, each stretching much further than telescopic searches can range. We can deduce that almost all such regions are probably hostile to life.